Hydration of silicates

ABSTRACT

THE INVENTION RELATES TO A PROCESS FOR HYDROCATION OF SILICATES WITH A LOW CALCIUM CONTENT-ONE MIXES WITH 2 TO 15% OF PORTLANT CEMENT AND 85 TO 98% OF SYNTHETIC MONOCALCIUM SILICATE HAVING AN ANALYSIS OF 35 TO 45% OF SIO2, 35 TO 50% OF CAO, 5 TO 15% OF AI2O3, AND UP TO 6% IN ALL OF ALKALI AND ALKALINE EARTH METAL OXIDE FE2O3, AND OTHER OXIDES, WHILST MAINTAINING A WATER/ SOLIDS RATIO OF 0.10 TO 0.4 AND AUTOCLAVING THE MIXTURE AT A TEMPERATURE OF 100 TO 250*C. UNDER A STEAM PRESSURE OF 1 TO 40 BARS.

AU 110 tax 3,717,488 HYDRATION OF SILICATES Regis Marie Albert Magnan, Montelimar, France, as-

signor to Societe Anonyme Ciments la Farge, Paris, France No Drawing. Filed Oct. 14, 1970, Ser. No. 80,782 Claims priority, applizzatiigrsolirance, Dec. 15, 1969,

Int. Cl. C0411 7/02 US. Cl. 106-97 11 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a process for hydration of silicates with a low calcium content-one mixes with 2 to 15% of portlant cement and 85 to 98% of synthetic monocalcium silicate having an analysis of 35 to 45% of SiO,, 35 to 50% of CaO, 5 to of A1 0 and up to 6% in all of alkali and alkaline earth metal oxide, Fe O and other oxides, whilst maintaining a water/ solids ratio of 0.10 to 0.4 and autoclaving the mixture at a temperature of 100 to 250 C. under a steam pressure of 1 to 40 bars.

The present invention relates to a process for the hydration of silicates with a low calcium content. It also relates to the hydrated monocalcium silicates so obtained as well as the mortars prepared and the various industrial applications of these products.

The applicant has previously developed a synthetic silicate which forms the subject of French Pat. No. 1,584,873 for: New monocalcium silicate, process for its manufacture and its applications. This synthetic silicate, which is designated in the said patent by the abbreviation CS may be obtained in the form of a product which is either vitreous or crystalline according to the type of cooling to which the initial mixture is subjected: The said CS has an oxide analysis of 45 to 60% silica, 30 to 45% lime and 0 to 15% of alumina, the last being present in the form of aluminium silicate or in the form of a silicate of calcium and aluminium, and may contain 0 to 3% of iron oxide with, also in the form of silicates, about 0 to 3% of magnesia and about 0 to 6% of K 0 and/orNa o, the silica/lime ratio being between 1 and 2 and preferably in the vicinity of 1.5. The CS has on the whole the properties of wollastonite or of pseudowollastonite and makes it possible, by the addition of aluminous cement, to obtain compressed concretes or mortars which may be used in the casting of moulded articles or the manufacture of simple shaped articles such as for example sanitary ware and tiles, using an appropriate value for the ratio W/C (water/cement).

It is known that the basis of the strength of portland cement is the formation of tobermorite or other hydrated silicates with a low calcium content during the hydration of the cement. The lime which is liberated at the same time ofiers little strength so long as it is not carbonated. On theother hand it is a deleterious element in certain respects contributing to the decomposition of concretes Patented Feb. 20, 1973 in pure waters, and the breakdown of portland cement concrete after heating. For this reason it would be of significance to find a product which only forms tobermorite when hydrated and this is a principal object of the present invention. It is also known that monocalcium silicate cement, as would be excepted, lacks any hydraulic properties, and that the synthesis of tobermorite may be carried out by suitable hydrothermal treatment of raw materials such as silica plus lime.

The first hydration tests carried out on synthetic monocalcium silicate not only confirmed that monocalcium silicate was effectively inert in relation to water under normal conditions, but they also showed on test-pieces made with a W/CS ratio equal to 0.15 that one obtained, after four hours in the autoclave at 215 C. and under 21 bars, the following strengths in barszvitreous synthetic silicate (S/L ratio (silica lime)1.l3) :20 bars; crystalline synthetic silicate (S/L ratio 1.13) 10 bars.

The X-ray diffraction examination showed that in the case of the vitreous product there was a vitreous phase present and in the case of the crystallised product pseudowollastonite and parawollastonite were present.

The present invention is based on the principle of catalysing the hydration reaction of the monocalcium silicate by means of certain portland cements or similar products and of subjecting the mixture to a thermal treatment, stoving or preferably autoclaving. It has been found that for a fairly wide range of different conditions both as to materials (different synthetic monocalcium silicates, diflerent portland cements, preferably with a high content of tricalcium silicate and advantageously very white, and different additives or auxiliaries, for example) as well as to procedures of treatment and utilisation, it was possible to obtain industrial materials providing inherently high strength and suitable for providing mortars endowed with exceptionally good qualities as compared with those of the mortars prepared from only the catalyst cements. Such results could not be obtained merely by use of the disclosure of the above mentioned 'French patent.

According to the invention, a process for the hydration of monocalcium silicates comprises intimately mixing with water 2 to 15% of portland cement and to 98% of synthetic monocalcium silicate having an analysis of 35 to 45% of SiO- 35 to 50% of CaO, 5 to 15% of A1 0 and up to 6% in all of alkali and alkaline earth metal oxide, F 0 and other oxides, whilst maintaining a water/ solids ratio of 0.10 to 0.4 and autoclaving the mixture at a temperature of 100 to 250 C. under a steam pressure of 1 to 40 bars.

It is found that, using portland cement, the lime contained in this cement is totally utilised during hydration to form tobermoritc, without any free lime remaining, which fulfils one of the principal objects of the invention.

The synthetic silicate used, which may be of the vitreous type or of the crystallised type, is preferably manufactured by the process described in the above mentioned French patent. For the portland cement employed as catalyst, it is preferred to use those cements which are currently known as superwhite and comply approximately to the following analysis:

It was observed that, generally speaking, better results were achieved using synthetic monocalcium silicates of the vitreous type than with the crystallised type, each type having the same silicate/ lime ratio in the neighbourhood of 1.13. Alternative portland cements may of course be used as catalysts as well as monocalcium silicates having different silica/lime ratios.

The results mentioned above, which have been the subject of numerous confirmatory tests, are not obtained if one does not use both the catalyst and a thermal treatment (stoving or autoclaving). Microphotographs and X-ray diffraction analyses carried out on the hydrated products obtained according to the invention show quite clearly well-crystallised tobermorite, the maximum content of which is an object of the invention.

The mixture can be subjected to a moist stoving of a duration of not less than 3 hours at a temperature greater than 80 C. on the whole, the duration of the stoving has an effect on the strengths of the final products, but this action varies according to the silicate employed: for a high ratio of silica/lime the stoving may be relatively short (upwards of 3 hours); for a low ratio of silica/lime the stoving must be prolonged (upwards of 5 hours), with the benefit of higher strength figures for certain silicates.

It is also possible to subject the mixed product to autoclaving.

The higher the temperature of this autoclaving, within the limits hereinbefore indicated, the more final strengths increase.

It is also possible, after the wet stoving or autoclaving, to subject the products to a passage through a dry stove for a period of 2 to hours at a temperature of 100 to 500 C.; this subsequent treatment has a favourable influence on the strengths of test-pieces of the product and confirms a high tobermorite content, especially in the case of the highest strength figures.

Besides portland cement, it is also possible to add to the synthetic silicate various supplementary additives of widely differing types, such as calcium chloride, CaCl calcium nitrate Ca(NO potassium or sodium carbonphate in the form of its semi-hydrate. The strengths obtained in the final product are then improved as compared with products containing only gypsum as an additive.

The particle size of the materials used is significant since this has an appreciable effect upon the strength of the products obtained. It is preferred to use finely divided materials, with to 80% passing through a 30; mesh. It has been found that the simultaneous grinding of the materials-silicate and catalyst(s)was particularly advantageous as compared with mechanical or manual mixing of the different materials after grinding.

Various examples are given below which show the properties of products obtained according to the method of the invention using a vitrified monocalcium silicate possessing the following composition:

Percent SiO 43.05 CaO 38.05 A1 0 11.90 Alkalis 4 with a silica/lime ratio of 1.13/1.

When dissolved in water this material gave a pH of 11.03 and liberated 72 mg. of CaO per litre.

The properties of a mortar on the basis of a 50%50% mixture of the said silicate and superwhite cement, as compared with a mortar made from superwhite cement alone are tabulated below.

Mortar according to standard P. 15-403 50% vitreous CS S/L=1.13; 2% rejected at 1.1 mm.; 50% superwhite portlaud cement.

Hydration tests on a mixture of the specified silicate and superwhite cement gave the following results: Mixture (80% vitreous CS S/L-l.13 (2% rejected at 0.1 mm.) 20% superwhite portland cement.

Tests carried out Strengths in bars X-ray diffraction:

Type of test pieces Treatment of test pieces Flexure Compression Examination Micro-pellets 1 made from the mixture 15 hours in damp air at 20 0. plus 8 hours autoelaving, of which 4 1, 030 0,811 1 alone with aratio water/mixtureOJfi. 2:11pm were slim 215 3nd mag erg. C 7 25 ours as ours amp a stand (Standards mm) 24 hours i n damp air at 20 0. plus 8 hours autocalaving. of which 4 10 410 with the mixture for binder. hours at 50 and 21 has 1 KeiI-Mathieu method. Tobermorite line at 11.5 angstroms MgOSm.

ate, lithium carbonate, gypsurn or sodium fluosilicate. A

preferred additive is gypsum, which shows optimum results when present to the extent of 2.5%; the actual addition of gypsum should preferably be between 2 and 5%.

The additive may comprise, in total or partial replacement of the gypsum referred to above, of calcium sul- Pellets for the tests, with a cross-section of 1 cm, with a height of 1 cm., were formed under a pressure of 500 bars. A water-mixture ratio of 0.15 was generally used.

A comparison between the behaviour of the vitreous and crystallised silicates is given by the folowing table.

Strengths in bars Pure paste with Mortar according to W/C=0.29 standard P 115-403 (W/C=0.5) Designation of the binder Flexure Compression Flexure Compression Mixture:

95% vitreous CS of 60% 40 S/L=1.13 superwhlto) 200 875 90 685 95% vitreous CS with 957 CS crushed with 60% 40;1S/L=l.3 (5% superwhi 125 430 35 180 95% CS crystallised 95% JS crushed to 60% 40pS/L=l.3 (5% superwhite). 65 215 20 95 Superwhite 135 450 110 735 The following test results indicate the combined influ- The action of Na S0 K 80 CaS0 0.5H 0 is illusences: trated by the following table. (1) of the type of CS (vitreous or crystallised) (2) of the silica/lime ratio of the cs mhmkm sum, (3) of the rate of addition; uCsS7(i7liclirene rlilaitgo Otherproducts in themixture (hairs)t aiiter [W 6 we S 0V ii of Superwhlte cement ceme nnperce nt p Compound Percent for 15 hrs. ofsoda 100 5:12 on the strengths after autoclaving. (Tests on micro-test- 32:}; pieces made with W/C=0.15, autoclaved for 4 hours at 2115 965: 215 C. at a pressure of 21 bars.) 2 872==28 2.5 Characteristics of the CS tested 1} 823* Type Calcium sulphate in the form of the semi-hydrate vitreous Vitreous fggg 5 appears to be the best additive.

The influence of the particle size of the components Silica lime ratio f a mixture f 1.0 1.3 1.3 Products added to Percent 92.5% vitreous CS (silica/lime ratio 1.13) and the CS emixture Compressionstrengths(inbars) 30 7.5% superwhite cement,

1 200 gm 3% and of the mode of preparing the mixture, on the strength superwhitecememm 2 13 23 510 of the product after 60 hours damp stoving at 95% C. CMOH)2 g 2% Egg 3 3 (pellets manufactured with W/C ratio=0.l5), is illustrated by the following table:

Particle size of the Particle size of the Strength Particle size of the CS superwhite cement mixture Method. of preparing mixture grinding the two products together (in bars) Less than 30p 60%-- Supergrinding oi the mixture indicated above admixture carried out 590 manually by means of a trowel.

' Very fine (in 850 Above 40; 100% Below 30 60% do 200 Lessthan 40,1 100%... Lessthan40u 1(X)% do 400 Less than 30 60%- Very fine .1 625 It will be seen that the rate of addition of white cement The influence of the silica/ lime ratio of the CS and may be quite low, 5%, and that the addition of Ca(OH), of the temperature of quenching of the mixture on the does not have the same function as the addition of portstrength of micro-testpieces of a mixture of 92.5% CS land cements. and 7.5% superwhite cement with 15% of water after damp stoving at 95 for 15 hours.

15 hours damp 15 hours damp stoving plus 2 stovin plus 24 15 hours damp hou(rs a%)500 hours 9r ying at stoving (n=9) 'm a m a m a" 562. 2 15. 5 1, 158. 3 110. 3 853 38. 6 525. 2 29. 5 1, 096. 6 45. 7 790 14. l. 546. 6 39. 7 995 59.1 796. 6 53. 0 568. 9 1'2. 8 l, 123. 3 86. 9 823 47. 8 535. 5 3 3. 4 1, 115. 0 104. 3 838. G 40. 2 After S/L=1.3 530. 0 6 l, 011. 6 72. 0 780 35. 6

Nora-m is the number of testpieoes, m is the mean compressive strength in bars and a is the typical discrepancy. The action of gypsum is illustrated by the table below.

Strengths in bars P t Aiteggamr; o C t Tests were carried out on a cement corresponding to Nature of the added ercen sto g a 95 or 86 product present 15 hours hours hours the following formula o e 0 475 gag CS (of the above mentioned type) percent by wt 90.2 Pure gypsum White cement of the above mentioned yp .percent.. 7.3 Gypsum (in 2.5 Calcium anhydrite Fineness: 65% particles 30[L The whiteness of the mixture reckoned against the 1 Gypsum containing 27.0% limestone burnt at 1,000 0. li h index p=83%.

Using this mixed cement, with mortar compositions have different W/C ratios, tests were carried out using (2) By semi-immersion in a 50 g./l. solution of both stoving and by autoclaving. MgSOf-n-Igo Seine sand Sand/ binder 0.16, 0.16-0.63, 0.63-1.25, 1.25-25, Flexural Comratio percent percent percent percent Treatment strength pression Setting 3 12 32 38 18 Stoving, 95 0., hours 48 200 Vibrating table. 3 25 25 20 29 Stoving, 95 C.. 6 hours... 42 250 Ramping. 2 25 21 29 Autoclaving, 3 hours, 215 860 Do. 2 25 25 21 29 950 Do.

1 After one month in damp air at 20 C.

Using prisms formed from composition (2), taking as initial measurements the length of the sample after treatment and after cooling;

with a sample of the same composition but auto- 30 claved, there was an expansion of 40 g/m.

The latter treatment therefore makes it possible to provide a mortar without hydraulic shrinkage.

On a sample composed and treated as per sample 3 of the table above, decomposition tests were carried out in different media. The results are summarised in the table which follows.

Strengths (bars) Observations Control prism after entoclaving.

Immersion in N110 H01:

Prisms scoured on the surface on the 4 faces.

3 months Immersion in M8804:

15 days n hs Control rism kept in damp air:

1 mon Semi-immersion in MgSOr: l

1 month Do 3 months 1 g. liter.

Of the testpiece which had been autoclaved and kept for 1 month in the air, the pH obtained by crushing it and dispersing the crushed paste in water was 11.0, 5

which suggests a good protection of the reinforcement.

Other tests dealt with the resistance to decomposition of mortars manufactured according to the invention. These tests were carried out on prisms of mortar with dimensions of 2 x 2 x 10;

(1) By complete immersion in a N/ 10 HCl solution in a N/10 NaOH solution in a 50 g./l. solution of MgSO -7H=O in pure water }Prisms intact. 50

The composition of the mortar used in these tests was as follows:

500 g. of binder comprising:

of monocalcium silicate with a silica/lime ratio 20 of 0.8 crushed to normal fineness 7.5% of Lafarge Super-white cement 2.5% of Prolabo gypsum 1000 g. of conglomerate comprising:

250 g. of Lemanoy sand 00.16 mm. 250 g. of fine Seine sand 0.16-0.63 mm. 210 g. of medium Seine sand 0.62-1.25 mm. 290 g. of coarse Seine sand 1.25-2.5 mm.

Comprmon strength In In In In In a 50 g./l. tmmerslon ordinary pure N 10 NM solution oi Iime after water water Cl NaOH MgSOtfl HO 15 days 773 892 1 month 790 1. 025 930 3 months- 944 998 750 1,040 1,008 6months..--- 965 978 691 1,014 1,042

One could therefore observe an excellent resistance in pure water, in the soda solution and in the solution of magnesium sulphate, as well as a good strength in acid solution, whereas:

A portland mortar would have been rapidly attacked if not destroyed by the acid, even though it would have stood up to the solution of soda. On the contrary, a mortar of Ciment fondu would have been attacked by the soda solution. According to its nature, a portland mortar would have stood up to a greater or lesser degree for 6 months in the solution of magnesium sulphate, although the Ciment fondu would have stood up very well.

In pure water all portland cements show a gradual fall in strength, as exemplified below.

5. A process according to claim 1, wherein wet stoving is carried out for more than 5 hours, and the silica/lime ratio of the synthetic monosilicate is 1.

Compression strength After 3 months After 6 months Emergent Immersed Emergent Immersed Binder used Part Part part part Appearance after 6 months CS in accordance with lnvention. 828 1, 008 908 1, 042 Absolutely intact, impeccable appearance of ceramic earthenware.

Control 864 864 Ciment loudu The strengths vary according to development, but No attack.

there was no attack.

CPA 400 without CsA 785 743 76 682 N0 visible attack. Control 726 794 CPA 400 with very low CQA 890 838 860 810 No visible attack. Control 852 859 CPA 400 with high content of C:A.. 760 752 640 Breakdown of immersed part. Control 742 738 CLK 564 7 Slig t attack of the emergent part visible. Control 502 558 The table above show the superiority after 6 months of the prisms manufactured in accordance with the inventron.

After 6 months the slag cements were attacked in the emergent part, whilst most of the portland cements and the cements on the basis of portland clinker are more or less attacked in the immersed part. Only the cirnent fondu showed no attack.

The behaviour after 6 months and the structure of the prisms manufactured according to the innvention (they have the appearance of an extremely compact and smooth ceramic earthenware) confirms the long-term existence of strength figures higher than those of the best portland cements.

The various tests carried out show therefore that by operating according to the invention, using a synthetic monocalcium silicate, a white portland cement and possibly another additive such as gypsum, there can be obtained, either by autoclaving and/or by stoving, mortars of a light colour possessing very useful properties both as regards their mechanical and chemical strength and sodiumfiuosilicate.

7. A process according to claim 6, wherein 2 to 5% of gypsum is added to the mixture.

8. A process according to claim 7, wherein at least a part of the gypsum is replaced by calcium sulphate in the form of its semi-hydrate 9. A process according to claim 1, wherein the particle size of the components of the mixture is such that 50 to 80% pass through a 30,11. sieve.

neously.

11. A process according to claim 1, wherein the synthetic monosilicate has 10. A process according to claim 1, wherein the constrtuents of the mixture are ground together simultaapproximately the following their dimensional stability. analysls: Percent The composition of the synthetic silicate, preferably A 2 3 it ifi d, is t critical, the most advantag D S102 tion being approximately A1 0 11%, sio 40%, lime CaO 49%. 50

What I claim is: References Cited 1. A process for the hydration of monocalcium silicates UN T STATES PATENTS comprising intimately mixing with water 2 to 15% of 3 505 439 4/1970 M h d portland cement and 85 to 98% of synthetic monocal- 3501324 3/1970 ea et 1O6 120 cium silicate having an analysis of 35 to 45% of SiO 3616116 4/1967 106 120 35 to 50% of CaO, s to 15% of A1 0 and up to 6% in 2547127 4,1951 all of alkali and alkaline earth metal oxide, Fe O and 2534303 12/1950 m- 106.120 other oxides, whilst maintaining a water/solids ratio of enms 106 120 0.10 to 0.4, and stoving or autoclaving the mixture at a FOREIGN PATENTS temperature of 100 to 250 C. under a pressure of 1 to 1,584,873 1/ 1970 F 40 bars of water vapour.

2. A process according to claim 1, wherein the silica/ lime ratio of the synthetic silicate is about 1.13.

3. A process according to claim 1, wherein the mixture is subjected to wet stoving for a period of 2 to 10 hours at a temperature of between 80 C. and 500 C. prior to a dry thermal treatment.

4. A process according to claim 1, wherein wet stoving is carried out for more than three hours, and the silica/ lime ratio of the synthetic monosilicate is 2.

OTHER REFERENCES JAMES E. POER, Primary Examiner US. Cl. X.R. 

